This invention relates to compact light sources and, more particularly, to a unitary light source comprising a compact HID lamp and incandescent ballast filament which are adapted to be operated from a household-type source of AC energizing potential.
HID lamps normally require a short period in which to warm up and build up pressure within the lamp, during which time the light output therefrom is limited. Also, after short periods of power interruption, the HID lamp normally cannot be reignited until the pressure therein has dropped. A system for supplying light during warm up and after power interruption is set forth in U.S. Pat. No. 3,749,968 dated July 31, 1973 to Jones et al. wherein a supplemental filament and HID lamp are enclosed within the same outer envelope. When the HID lamp is warming up, or is not operating such as after a period of power interruption, the incandescent filament is operated with full intensity to provide light. After the HID lamp is operating normally, the potential developed across the filament is substantially reduced.
Miniature-type HID metal halide lamps can operate with a high efficacy, as disclosed in U.S. Pat. No. 4,161,672 dated July 17, 1979 to Cap et al. and U.S. Pat. No. 4,170,746 dated Oct. 9, 1979 to Davenport. Various circuits and arrangements for operating such lamps in conjunction with a light-emitting filament which can also serve as a ballast or current limiting impedance for the HID lamp are disclosed in U.S. Pat. No. 4,170,744 dated Oct. 9, 1979 to Hansler and U.S. Pat. No. 4,151,445 dated Apr. 24, 1979 to Davenport et al. Such lamps are also summarized in New York Times article June 15, 1979 page D3 and Business Week, June 25, 1979, pages 35 and 36.